Update pubsub spec to describe the push-transports property and APNs


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@14126 e27351fd-9f3e-4f54-a53b-843176b1656c
Updated spec.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@14127 e27351fd-9f3e-4f54-a53b-843176b1656c
Pulled up r14095 from trunk.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@14128 e27351fd-9f3e-4f54-a53b-843176b1656c
Pulled up r14117-9 from trunk.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@14129 e27351fd-9f3e-4f54-a53b-843176b1656c